Fluid catalytic cracking (FCC) processes originally used high alumina catalysts. In these processes, the hydrocarbon load was mixed with the fluidized catalyst and piped into a riser. The riser discharged the reaction products mixed with the catalyst onto a fluidized bed to bring a halt to the reactions.
The FCC processes next began using zeolite catalysts. Because they were more active than the alumina type, there was no longer the need for a catalytic bed.
Subsequent systems involved a longer riser so as to ensure the ballistic or inertial disengagement of the catalyst (“all riser cracking”).
The technique was improved by the introduction of load dispersal devices and by pre-accelerating the catalyst to boost catalyst-load contact.
These improvements made cracking in the riser more selective and vigorous, leading to the need for more efficient devices for disengaging the products and the spent catalyst.
One solution for the technique involving this disengagement is to install cyclones directly coupled to the riser outlet.
Closed cyclone systems then emerged, aimed at reducing thermal overcracking due to hydrocarbons passing through the disengager vessel and the lengthy contact time between solid and gaseous particles. These systems made it possible for reaction products to go directly from the riser to the transfer line through cyclones with a shorter residence time of approximately one second or less.
The technique draws from various publications based on the concept of closed cyclones.
Some publications describe closed cyclone disengaging systems comprising cyclones fitted with a sealing leg for holding in the collected solids.
Other publications deal with closed disengaging systems that have a cyclone directly connected to the riser and with no sealing leg, and with a lower nozzle opening directly into the disengaging vessel, and which does not retain the disengaged solids.
Solids disengaged by the legless cyclone are discharged through its lower nozzle, with the large volume of the disengager vessel serving to reduce pressure variations in the riser.
The Applicant's Brazilian patent PI 9303773, illustrated in the attached FIG. 1, describes a closed and unconfined cyclone disengaging system, comprising a disengager vessel 19 fitted with a cyclone 12 without a sealing leg directly connected to the riser 11, with the lower end of said cyclone 12 opening up directly into a large-volume disengager vessel 19.
Optionally, the lower nozzle of the cyclone 12 may contain one or more distributors 12a of solids to improve passing of the downward flow of the disengaged catalyst particles.
The legless cyclone 12 is interconnected to a primary cyclone 17a through concentric pipes 16a, 16b. The connection between the primary cyclone 17a and the secondary cyclone 17b is comprised of piping 18a. 
Disengaged gases exit from the disengager vessel 19 through the outlet duct 18b. The annular space 15 between the pipes 16a, 16b connects the piping interior to the disengager vessel 19. Gases from the disengager vessel 19 drain through this opening. The purge liquid injector devices 10 help to drain the stagnated gases in the disengager vessel 19.
The Applicant's Brazilian publication PI 9901484, illustrated in attached FIGS. 3a and 3b, describes a device for controlling the flow of liquids through the annular space of telescoping joints 35, as well as how to employ this device. The device accordingly comprises a slip ring 35a coupled to connection ducts 34, 36 to ensure there will be an annular section with constant spacing in the area where the connection ducts 34, 36 are joined, with no structural damage from yielding to movement produced by changing temperatures.
Use of the slip ring 35a coupled to the telescoping joint 35 ensures a constant area for the passing of liquids and a controlled load loss to accommodate a given flow of liquids.
The Applicant's Brazilian publication PI 0002087, illustrated in the attached FIG. 2 describes a closed, unconfined cyclone disengager system, improved with flow distributors 26a, 26b to balance the gases coming from two or more cyclones in the same stage or between different stages.
FIG. 2 illustrates a right-angle sectional cutaway view of the disengager vessel 29 of an FCC unit wherein two first-stage cyclones 22 are connected to a flow distributor 26a. 
The first-stage cyclones 22 are interconnected to the second-stage cyclones 27 through interconnection ducts 26b. There is a narrow passageway 25 in the interconnection duct 26b providing an outlet for the steam injected into the riser and the rectifier, as well as allowing some of the rectified hydrocarbons to be drawn off.
Steam is injected into the rectifier and the riser under various predetermined flows, programmed in accordance with unit operating conditions.
This procedure ensures a proper pressure balance around the legless cyclone, making it possible to alternate between purging and bleeding.
Purging is carried out under flow conditions, with a slight amount of steam from the disengager vessel 29 entering the legless cyclone 22 through the lower solid discharge nozzle.
Bleeding under flow conditions occurs with a slight amount of gas passing from the legless cyclone 22 into the disengager vessel 29.
In the system described in Brazilian publication PI 0002087, the overall efficiency of solid collection is considerably higher.
The use of technology for solid-gas disengaging through closed, (unconfined) legless cyclone systems in FCC processes described in the Applicant's Brazilian publications PI 0002087 and PI 9303773, included herein as references, reduces thermal cracking caused by the hydrocarbons passing through the disengager vessel, with highly efficient overall solid collection.
However, with these systems as described in prior art, even under purge conditions, most of the steam injected into the riser and the rectifier along with the hydrocarbons coming from rectification is captured through the nozzles located on the interconnection duct between the legless cyclone and the upper cyclone, or through a telescoping joint, with a smaller amount captured through the back flow passing through the lower end of the legless cyclone.
In addition, owing to the fact that most of the hydrocarbons are confined inside the cyclones, the area of the disengager vessel above the lower end of the legless cyclones has a lower temperature, inasmuch as virtually none of the currents with most of the energy (catalyst and hydrocarbons) pass through this part of the disengager vessel. Accordingly, the area between the lower end of the legless cyclones and the top of the disengager vessel has a negative temperature gradient; at the end of an operating run the top and bottom of the disengager vessel may show a temperature difference of as much as 100° C.
Under these conditions, the low remaining flow of hydrocarbons circulates through a part of the disengager vessel with a lower temperature before reaching the telescoping joint or the nozzles on the interconnection duct between the cyclones. Passage of these hydrocarbons through this cooler area of the disengager vessel, along with their extended residence time inside the vessel, enhances condensation and thermal cracking, which cause coke deposits to form inside the disengager vessel over time. This factor poses a risk for operating continuity of the converter, inasmuch as the loosening of pieces of coke could hamper circulation of the catalyst by blocking the rectifier and/or the standpipes.
One attempt to solve this problem, contained in prior art, is illustrated in the attached FIG. 3C, is described in the Applicant's patent application PI 0203419-0, which uses a legless cyclone 32 fitted with internal piping 33, said piping 33 having open ends. Patent application PI 0203419-0 utilizes a telescoping joint (not shown in FIG. 3C) in the riser inside the disengager vessel, required in order to accommodate thermal expansion. It should be mentioned that this combined solution does not apply to FCC converters whose riser is outside the disengager vessel.
Although this alternative reduces the problem of coking by capturing the hydrocarbons in a place beneath that where the gases described in the prior art are collected, it does not solve the problem efficiently, since it creates another related problem: release of the catalyst.
The piping 33 inside the legless cyclone 32 collects the gases coming from the disengager vessel, releasing part of the catalyst from the legless cyclone 32 into the internal piping 33, said catalyst being carried to the cyclones of the following stages. This release of catalyst reduces overall disengaging efficiency, increasing the concentration of solids in the disengager vessel effluent, as well as further eroding the cyclones in the following stages, which could significantly reduce run time for the unit.
This release hampers the disengagement stage between the spent catalyst and the hydrocarbons, since it carries the catalyst that had previously been disengaged by the legless cyclone 32 on to the next stage.
The catalyst fraction released into the piping 33 inside the legless cyclone may also lead to erosion of the piping 33 interior.
Another problem created by the fact of having piping inside the cyclone is that if the piping is punctured—which can happen at any time during the run owing to erosion—such will reduce the efficiency of the legless cyclone 32 because the solids inside of it will be shunted directly to the cyclones in the following stages.
Accordingly, the systems described in the prior art fail to efficiently solve the problem of coke deposition in the disengager vessel.
Coke deposition in the disengager vessel reduces the operating reliability of the unit, due to the constant risk of problems linked to hampered catalyst circulation caused by pieces of coke breaking loose. Moreover, maintenance (scheduled or otherwise) is more costly, because of the time it takes to remove the coke that has stuck tightly to the walls of the disengager vessel and its inner components.
Accordingly, the technique also requires a cyclonic system and a process for disengaging solid and gaseous particles in FCC processes that reduces coke formation without lowering disengagement efficiency nor threatening the integrity of the cyclones, with said system and process described in the body and claims of the present patent application.